A UN nuclear watchdog team is now in Tehran for talks.
The trip by the International Atomic Energy Agency to Iran comes ahead of this month's deadline to create a political agreement between Iran and the so-called P5+1.
Among the discussions expected between the IAEA and Tehran is potential access to Iranian nuclear sites.
This has been one of the key sticking points in negotiations to create a long-term nuclear deal with Iran.
Behrouz Kamalvandi is the deputy head of Iran's Atomic Energy Organization.
"The topic is the previous explosions that are claimed to have taken place in Marivan. We have said it many times verbally, in writing and in our meetings, that we are ready to give access to the agency to come and see for themselves that these allegations are baseless."
However, the IAEA has been pressing for access to the Parchin military base southeast of Tehran.
This is where it suspects other nuclear-related testing may have taken place, including a possible nuclear weapons test a decade ago.
Tehran has refused the IAEA access to Parchin, citing security concerns, as it is also a conventional military facility.
Iran has long insisted its nuclear program is strictly for civilian purposes.
